1. Field of the Invention
The present invention relates to a fuel check valve assembly for use in a fuel tank of an automotive vehicle or the like.
2. Description of the Prior Art
As is well known, some automotive vehicle fuel tank is equipped with a fuel check valve assembly for preventing outflow of fuel from the fuel tank through a vent line of an evaporative emission control system when the surface of fuel inclines relative to the fuel tank. The fuel check valve assembly is installed within the fuel tank and includes a float valve which, when the surface of fuel inclines relative to the fuel tank and fuel is caused to flow into the fuel check valve assembly, moves upward by the effect of its buoyancy and closes a valve seat for thereby preventing outflow of fuel from the fuel tank through the vent line of the evaporative emission control system.
In such a prior art fuel check valve assembly, when the pressure differential between the inside of the fuel tank and the inside of the vent line becomes large, there arises a tendency that the float valve is kept sticking to the valve seat even after the fuel check valve assembly is drained off. In order to prevent such sticking of the float valve, it has been practiced to employ a large-sized and heavy float valve, thus leading to a problem of an increased weight of an automotive vehicle, etc.
In order to solve this problem, such a fuel check valve assembly as disclosed in Japanese Utility Model Provisional Publication No. 62-75278 has been proposed. This fuel check valve assembly is provided with a relief valve which, when the pressure differential between the inside of the fuel tank and the inside of the vent line of the evaporative emission control system increases beyond a predetermined value, opens for releasing fuel vapors from the fuel tank for thereby lowering the pressure within the fuel tank and preventing the float valve from sticking to the valve seat.
The pressure differential in response to which the relief valve is caused to open, needs to be set lower than the pressure differential (hereinafter referred to as stick pressure) in response to which the float valve is caused to stick to its valve seat. When the stick pressure of the float valve is low, such a case may occur in which normal closure of the float valve causes the relief valve to open. It is therefore desirable to set the stick pressure as high as possible. For this reason, the float valve is still necessitated to be large-sized and heavy. The fuel check valve assembly disclosed by the above described Japanese Patent Provisional Publication therefore cannot provide a means for solving the above noted problem completely.